This invention relates to semiconductor III-V alloy compounds, as well as to a method of making III-V alloy compounds for use in two-color detectors.
Infrared (IR) detection is used in many military and commercial applications such as pollution monitoring, night vision, missile tracking, and seeker-tracer systems. The detection of infrared electromagnetic radiation can be accomplished by utilizing either thermal or photon detectors. Photon detectors use narrow bandgap semiconductors, with carriers being generated through the excitement of electron and holes by incident light with energy higher than that of the material bandgap.
Most established infrared imaging systems are single color detectors, meaning that the response of the detector is designed to cover a single region of the IR spectrum. Single color detection is suitable for many applications, but is not adequate for accurate temperature determination or for reliable object identification of objects with unknown emissivities. Two-color detectors are detectors with photoresponse in two separate spectral regions which can eliminate the need for knowing specific object emissivities.
Existing technologies for two-color detection utilize stacked diodes with different active regions which responds to different wavelengths of light, such as superlattices with different well thicknesses and/or band offsets, or by using compound semiconductor materials with different bandgaps. The former method is rather complex, requiring accurate modeling and very large numbers of layers in the structure, and the latter can have the problem of lattice mismatch because of the requirement for different bandgap active regions. The active region could be a ternary or quaternary material, or a superlattice structure. In either case, lattice matching is very important for higher performance detectors, and the fabrication is quite complex. The device is a three terminal device which also adds complexity to the circuitry used to read out the detector electrical signal because of the need for three connections to every pixel.
These and other objections are attained by the subject invention wherein a heterostructure having lattice matched layers with different bandgaps is grown by MOCVD or like process. More specifically, a wide bandgap material such as AlInSb or GaInSb is grown on a substrate to form a lower-contact layer. An n-type active layer is lattice matched to the lower contact layer and doped. The active layer is a narrow bandgap material, such as InAsSb. A p-type upper contact layer is then grown on the active layer doped and the structure is annealed.
An object, therefore, of the subject invention is a two-color detector.
A further object of the subject invention is a two contact device with a narrow bandgap in an active layer.